The present invention relates to a novel polycarbosilane and a method of producing the same.
A polycarbosilane has attracted attention as a precursor for silicon carbide fibers and ceramic materials, and has been industrially utilized. In particular, a polycarbosilane having a main chain with a repeating structure of silicon atoms and carbon atoms exhibits excellent heat resistance and is widely utilized. The polycarbosilane is expected to be applied to optical functional materials, conductive materials, and the like.
As a method of producing a polycarbosilane having a main chain with a repeating structure of silicon atoms and carbon atoms, a method utilizing thermal rearrangement of poly(dimethylsilane) (Journal of Materials Science, 2569 to 2576, Vol. 13, 1978) can be given. According to this method, some methyl groups bonded to silicon atoms in poly(dimethylsilane) are inserted into Si—Si bonds in the main chain to form Si—C bonds, and the rearranged Si—CH3 sites are replaced with Si—H bonds.
As other methods of producing a polycarbosilane, a method of producing a polycarbosilane from chloromethyltrichlorosilane through a Grignard reaction (Organometallics, 1336 to 1344, Vol. 10, 1991), and a method of producing a polycarbosilane by ring-opening polymerization of a disilacyclobutane (Journal of Organometallic Chemistry, 1 to 10, Vol. 521, 1996) can be given. These documents disclose a method of producing a polycarbosilane containing an Si—H bond by replacing a substituent on a silicon atom in a monomer with a chlorine atom, polymerizing the monomers, and reducing the resulting polymer by using lithium aluminum hydride or the like.
In related-art technology, a polycarbosilane is generally cured by (1) formation of Si—O—Si crosslinks by sintering in an oxidizing atmosphere (U.S. Pat. No. 5,602,060 and US-A-2003/17635) or (2) formation of Si—Si bonds by coupling between Si—H bonds and subsequent formation of Si—C—Si bonds by a rearrangement reaction (US-A-2003/17635). However, when the method (1) is utilized for a semiconductor integrated circuit manufacturing process, metal interconnects provided on a substrate may be oxidized so that the interconnect resistance may be increased. In the method (2), the curing reaction more easily proceeds as the content of the Si—H bonds in the polymer becomes higher. However, a dehydrogenation coupling reaction gradually occurs during storage, whereby the polymer may deteriorate.
As a polycarbosilane which solves the above-described problems, can be cured under reduced pressure or an inert gas atmosphere, and is chemically stable, (1) a polycarbosilane which is readily cured by heating or the like due to the presence of a crosslinkable side chain other than the Si—H bond or introduction of a mildly crosslinked structure before crosslinking, or (2) a polycarbosilane which further contains an appropriate amount of Si—H bond side chains to enable the dehydrogenation coupling reaction is preferable. In the case of a polycarbosilane which can be cured by only the mechanism described in (1), the amount of crosslink site in the polymer is increased. As a result, thermal stability and mechanical strength may be decreased when the crosslink site is an organic group, or resistance to processing such as etching and plasma processing may be decreased in semiconductor integrated circuit applications when the crosslink site is a siloxane structure. US-A-2003/17635 discloses a method of applying a polycarbosilane which does not contain an Si—O bond to a silicon wafer and heating the applied polycarbosilane in air to form an Si—O—Si bond by oxidation, and JP-A-2003-142477 and JP-T-8-510292 disclose polymers obtained by modifying a polycarbosilane containing an Si—H bond in an organic solvent by using alkali and water. However, a polycarbosilane which does not affect other materials such as interconnects when applied to a semiconductor integrated circuit manufacturing process and exhibits excellent storage stability has not yet been obtained.